We make large and small sensitive non-contact ammeters, mostly clamp-on, called Swain Meter.RTM., to measure DC and/or AC flowing in conductors from #22 wire to 60 inch diameter pipe.
Basic concepts are shown in U.S. Pat. No. 3,768,011: "Means for measuring magnitude and direction of a direct current or permanent magnet, including clip-on direct current sensing inductor".
Improvements (MER Meter and MEC Meter) are described in U.S. patent application Ser. No. 08/579,395: "Error Correction by Selective Modulation".
DC Amp Clips are described on the website of the William H. Swain Co: www.SwainMeter.com
Some time ago I received a call from Paris asking about permanent installation of a sensor clamp at the base of a 13 inch pipe on an oil producing platform in a lake in Africa. In effect I declined because of the possibility of unexplained readings at the output of the indicator on the surface. I did not know how to economically find out if the clamp was still working well, or was damaged to where it could not be trusted.
To answer this question, I have discovered, designed and built a machine called Rgage.TM. for estimating the reliability of a non-contact ammeter by measuring and comparing the merit of its parts with references. Rgage is also useful for improving the quality of new meters, measuring the quality of meters in calibration or service, preferably without seriously disturbing their normal function, and locating and appraising damage should it occur. Hence the name "Reliability Gage for non-contact ammeters", or Rgage for short. The process for making an Rgage machine has been generalized to where it will be useful for ammeters other than Swain Meters.
I use the word reliable in the sense that the Swain Meter can be counted upon to do what is expected--provide an accurate measure of the electrical current flowing in the aperture of the sensor.
This definition of "reliable" is from webster. I am also aware of the science of Reliability assessment, partly in terms of component failure rates, etc. This is outside the scope of my invention. I here use the word "reliable" as I believe was intended by a customer when he said "I think the (newer) MER Meter is much more reliable". He appreciated a dependable, accurate and user-friendly clamp-on ammeter.
Swain Meters have proven reliable--beyond my expectations--even when buried in earth or used subsea. The Rgage has been built for assurance that a specific ammeter is now reliable and is expected to stay that way.
This patent application teaches how to estimate reliability for future use, locate a fault, and assess the present best use of a faulty non-contact ammeter.
Rgage is also for a production quality control tool for a calibration lab or a repair facility. Typical 2 wire in--2 wire out construction facilitates installation and removal.
The Rgage process includes measuring specific merits which are indicative of the quality or value of parts or parameters. An example is the total sensor plus cable DC resistance .SIGMA.r.sub.s. The measurement is preferably automated, with computer control and analysis of the "spreadsheet".
Measurements are normalized and compared for inclusion in a "Rgage spreadsheet" or computer file equivalent. Results are combined, correlated, and processed with design and experience reference files of merit magnitudes representative of a clean or faulty ammeter so as to output estimated reliability, fault location, and assess present use.